1. Field of the Invention
The present disclosure relates to a technique in which a lane is detected based on imaging data taken by a rear camera that captures an image of a rearward field of view of a vehicle and, in particular, a traveling lane selected by the vehicle is identified when the number of lanes changes.
2. Description of the Related Art
There have been systems that have imaging cameras that capture images of imaging forward, rearward, side fields of view and the like connected to a vehicle onboard unit having a navigation function and provide guidance to a driver by displaying images taken by the imaging cameras on a display or the like of the vehicle onboard unit, and such systems are widely used. In particular, an image taken by a rear camera is an image of a rearward field of view, which is the most difficult for a driver to see, and such an image allows for an easier driving operation when the driver parks the vehicle in a garage. Further, an image taken by a rear camera is useful not only from a driver's point of view but also for internal processing of various functions, such as determining a traffic state based on the image.
Techniques for detecting a lane change and/or a traveling lane by using an image of a forward field of view and/or a rearward field of view have been disclosed. Japanese Unexamined Patent Application Publication No. 2013-181959 discloses a vehicle onboard unit that recognizes left and right white lines based on an image of a forward field of view or a rearward field of view during traveling and, based on the recognized white lines and a traveling lane estimated before a boundary point of divided lanes, estimates a traveling lane after passing the boundary point of the divided lanes. Japanese Unexamined Patent Application Publication No. 2010-281781 discloses a lane change detection device that measures an inclination angle of a lane boundary line, detects a lateral move of a vehicle based on the measured inclination angle, a vehicle speed, and the like, and detects a lane change when the amount of the lateral move exceeds a predetermined distance. Japanese Unexamined Patent Application Publication No. 2010-221859 discloses a vehicle driving support device that estimates the type of a white line based on driving history information even when the type of a white line cannot be recognized due to aging, dirt, or the like. Japanese Unexamined Patent Application Publication No. 2005-4442 discloses a traveling lane determination device that extracts a predetermined area of an image and determines the type of a traveling lane based on image information included in the extracted area.
In an electronic device having a function of detecting a traveling lane based on imaging data taken by an imaging camera, a traveling lane of a vehicle is identified by an image recognition of lane demarcation lines (also, referred to as white lines) occurring in both sides of the vehicle. Further, when a vehicle moves from one lane to another, the electronic device detects the movement of lanes when the vehicle passes over a white line.
In the method of detecting a white line to detect a traveling lane of a vehicle, however, the following problems arise. When lanes are changed at a dividing point where the number of lanes increases such as at an intersection, there is a case where a lane demarcation line to be passed is out of sight of an imaging camera and thus a traveling lane of a vehicle cannot be recognized. FIG. 8 illustrates a situation where a vehicle M moves from one lane to another at a dividing point where the number of lanes increases. An imaging camera C that captures an image of a rearward field of view is mounted on a vehicle M (hereafter, referred to as M1, M2, or M3 based on a position of the vehicle illustrated in FIG. 8). When the vehicle M1 traveling on a lane R2 moves to an additional lane R1, there occurs a state where no lane demarcation line is taken by the imaging camera C for a certain period of time. That is, there is no lane demarcation line demarcating the lanes R1 and R2 at the dividing point where the lane R1 is divided from the lane R2, and thus only a white line L that is the boundary between the lane R1 and the lane R2 appears in an imaging area A2 that is taken by the imaging camera C of the vehicle M2. When the vehicle M3 fully moves to the lane R1 to travel on the lane R1, the white line L that is the boundary between the lane R1 and the lane R2 appears in an imaging area A3. In such a way, in the conventional identification of a traveling lane, since the white line L is detected after the vehicle M3 travels on the lane R1 for a while and the traveling of the vehicle M3 is identified based on the detection result, a quick identification of a traveling lane is not performed at a dividing point.